A conventional ultrafine wire is made of metal or alloy. However, when a diameter of the ultrafine wire is 1 micrometer-50 micrometers, a tensile strength of the ultrafine wire will be significantly reduced.
Since carbon nanotubes have good mechanical properties, the carbon nanotubes are widely used to make an ultrafine wire. A conventional carbon nanotube wire comprises a plurality of microscopic carbon nanotubes connected to each other. Although the carbon nanotube wire has high mechanical strength, the connection between adjacent carbon nanotubes has high resistance, and the conductivity of the carbon nanotube wire can be improved.
In order to improve the conductivity of the carbon nanotube wire, the surface of the carbon nanotube wire is coated by a metal layer with a thickness of 1 nanometer to 50 nanometers. Comparing to the carbon nanotube wire consisting of carbon nanotubes, the electric conductivity of the carbon nanotube wire with the metal layer is improved. However, the metal layer is thin, and is easily oxidized, so the durability of the carbon nanotube wire is low.